Batch for refractory masses and method of consolidating



Sept. 18, 1951 F. E. LATHE BATCH FOR REFRACTORY MASSES AND METHOD OFCONSOLIDATING 7 Filed Aug. 5, 1946 4 Sheets$heet 1 Qa uh m m & n W5 1%mi M a Nfimw F. E. LATHE Sept. 18, 1951 BATCH FOR REFRACTORY MASSES ANDMETHOD-OF CONSOLIDATING 4 Sheets-Sheet 5 Filed Aug. 5, 1946 .1 w 0 ..O mm H 0A a a O D O O 0 0 O m m m w W w. w W. m m n n n w n T r r r ruomimk F. E. LATH E 2,568,237

4 Sheets-Sheet 4 10 70:30 mic l'rfEfi CLAY In v-en iamfi-Ziarney,

WEIGHT PERCENT s i 0 Mao-1;

BATCH FOR REFRACTORY MASSES AND METHOD OF CONSOLIDATING ept. 18, 1951Filed Aug. 5, 1946 Q "9 IO 20 M o(5a.-4-2) CALC/NED DOLOMITE woo 2. .I aw m m 0 0 M w m w n w w m w w w w w w a a 2 w as 2 2 2 2 2 m Ua msmlb 40WE/G-HT CALC/NED CLAY Patented Sept. 18, 1951 BATCH FOR REFRACTORYMASSES AND METHOD OF CONSQLIDATING Frank Eugene Lathe, ttawa, Ontario,Canada, assignor to Canadian Refractories Limited, Montreal, Quebec,Canada, a corporation of Canada Application August 3, 1946, Serial No.688,264

In Canada July 16, 1946 7 Claims. (Cl. 1016-57) This invention relatesto the. bonding of refractory materials, and in particular to a methodofconsolidating granular particles of refractory character, at arelatively low temperature, into highly refractory masses and shapes.

In the industrial application of refractoriesas, forexample, in formingfurniace bottoms and in fettling open hearth and electric steel furnacebanks-it is highly advantageous to use materials which will set" or bewell consolidated, at a relatively low temperature. This will obviatethe necessity of driving a furnace so hard as to damage thesuperstructure by partial fusion of the brickwork, which is a frequentresult when material, too refractory in character, is to be consolidatedin the furnace lining. By reducing the maximum temperature required, andshortening the period of-burning-in the bottom, important economies inboth fuel and labour can be effected. By producing a more monolithicbottom, the absorption of steel and slag will be reduced, and the usefullife of the refractory will be increased.

On the other hand, it is obviously important to have furnace liningsmade of materials sufficiently refractory that they will not fail at thehighest working temperature. With the development for furnacesuperstructures of materials substantially more refractory than havepreviously been used, and the higher operating temperatures adopted as aresult, the danger of breakouts and other types of hearth failure hasbeen increased. lhis continued trend towards higher temperaturesemphasizes the need for improvide hearth refractories.

It will be seen that these two desiderata in the properties ofrefractories-consolidation' at low temperature and resistance to failureat high temperature-are diametrically opposed. It is not too' much tosay that for the past twentyfive years a major objective of research onrefractories has been to devise ways and means of overcoming thesedefects. Much ingenuity has been shown in effecting compromises betweenthe two objectives.

In the older practice, when it was desired to make a permanent hearthfrom Austrian mag-' nesite or other form of highly refractory periclas'eclinker (which cannot be burned to a monolithic mass at any permissibleor readily attainable temperature) it was customary to mix with theclinker some 20-25% of slag, the purpose of which was tomelt at arelatively low temperature and thus act as a bond for the morerefractory particles of periclase. However, the ultimate product was atbest a mixture of the two materials-used, and the slag matrix remainedas a weak componentfor an indefinite period, being subject to melting atmaximum operating temperatures, to chemical attack by the constituentsof the furnace charge, and to physical replacement in the bottom bymolten steeL, Such practice, while still followed to some extent, hasbeen largely superseded by more modern methods.

A major improvement was effected by the development of "magnesiteclinkers containing, as essential constituents of the clinker particles,9. sufilcient proportion of compounds of lower refractoriness, such ascalcium ferrites and aluminates, to constitute a. self-bonding material.These have been called thermoplastic hearth refractories. jMcAnally (U.S. 1,305,475) used in his clinker 16-18%.015 lime and 8.0-8.5% of ironoxide plus alumina. His product could be sintered to a monolithic masswithout the addition of slag, and has been widely imitated, but in hismethod improved setting was secured at the expense of, ultimaterefractoriness, since any fluxes introduced become a permanent part ofthe hearth, and are converted to the liquid condition whenever thetemperature rises sufliciently high. Using the same principle, McCaugheyand Lee (U, S. 1,965,605) introduced similar proportions of calciumferrites and aluminates into a clinker; of higher magnesia content.Seaton and Hartzell (U. S. 2,218,485) used two different magnesiarrefractories, of such composition and in suchgproportions that, by theirreaction with one another, dicalcium silicate, tricalcium aluminate andcal-, cium ferrite were said to be formed. The addition; of slag to bondsuch refractories was recognized as desirable, and in'fact was claimed.Later (U. S. 2,238,428), these investigators produced a refractorycontaining a minor proportion of monticellite (CaO.MgO.SiO2), and thenconverted the, latter to dicalcium silicate (2CaO.SiO'2) by heat; ingthe refractory with a lime-bearing material. Lee (US. 2,292,644)similarly improved there? fractoriness'of a. material containingmerwinite (3CaO.MgO.2Si02) by adding lime and heating. to convert atleast a part of the merwinite to di-f calcium silicate. Lee objected to,the presence inj the primary refractory of monticellite, which, lie

said, lowered the'refractoriness too much.

In summary, it has previously been proposed-.:

to make refractories which would set atattain able temperatures by (1)using in furnace'linings mixtures of slag and refractories high in-magnesia, (2 introducing calcium ferrite and alumi;

mm? satee c r mbi gla' Recently, a different method pfj attach on the,problem has been made by the"introtluctiori of,

chemical bonds, such as sodium silicatef into masses of refractoryclinker that are rammed into place, and thereby beeomes,-unnecessary togive the material a prolonged heat"treatment at high temperature inorder to form a working bottom. This development has-proved; o f,.greattimportance in saving time and thereby increasing;

plant capacity, but it has not overcome the difficulty involved in themtroduction of constituents of low melting-point, and refractories ofthis type have'been too expensive for general use in mam; taming-furnacebanks}. 1

1% the latter purpose, so-c alled double-burned dolomite, containing aconsiderable proportion of iron-oxide, has'been -extensiyely used, alongwith raw ar id calcined dolomite, but 1' these materialsaiiord"onlytemporary protection-tofurnace bank-sand their chifmeritisini'act their cheapness.

' Inno case, it must-beemphasized, do these proposals-overcome'both ofthe major difficulties set out above; and at best theyconstituteonly'various degrees of compromise. Some methods do not'sufiiciently lower the setting; temperature to effect maj oreconomiesin' burningin the-original harths or injfettlingfurnace banks;some per manently lower the r'efracto'ririess of the furnace materialsto such a degree that subsequent service' is: impaired. In spite oftheirindividual advantages, the problem remains essentially thesame'-that of developinga material which will set rapidly at easilyattainable temp'eraturesfand which will nevertheless have 's'ufiici'entultimate refractoriness to permit raising thefoperatin'g temperature toa point well above't-hat now used. Heretofore, 'no such material hadbeen 'produced; 'In' the accompanyin drawingsare s'how'nmelt ing-pointdiagrams of Y actuar or hypothetical starting materials of the characterherein described to facilitate a ready understanding of the invention.The temperatures given herein are mgeneme'ither those compiledby-'Sosman and Andersen, as given'on U; 'S'I'Steel Corporation Plates1-4 Composition -'Temprature Phase Equilibrium Diagrams of theRefractory Oxides, dated Octoberf1933, or those given incomprehensivereviews by Hall and Insley, Degrees. c'entie grade are usedthroughout;

accordance with: the present invention an entirely newapproach to theproblem hastherefore been made and, as willbeseen'belowit has been foundthat'bothf difiiculties can be overcome by. simple and highly'fe'conomical me'ans." Not only is the consolidation of highlyrefractoryparticlesfib'rought about at alsubstantially lower tem- Pe e qet nmeihere ofo e' b n q isible w -I outthe'introdiicti 'or alkali metalcompounds, but the ultimate 'refractoriness of the furnace liningor'refractory-"shapes is at the same time ub' iana t h ed In order to'accomplish these desirable ends, it is'essential toselectparticularist'arting materials. hese i m ea co i 'i'd l var ty of ari 1.1: ii r qiimine a nd' f those combinations may it use'd'which belong tooral emanate, but only;

4 a very specific type. This acceptable type is invariably characterizedby (1) reaction between the starting materials, under suitableconditions, to form a definite chemical compound of high refractoriness,and (2) the, formation between this chemical compoundand onei'of thestarting materials-but not the otherof a product (usually of eutecticcharacter) which substantially or completely melts to a liquid conditionat thelo'w temperature desired. That is, the temperature of liquidformation between the compoundand one starting material must always bemuch below that of any eutectic or other liquid which may beformedbetween the compound and the second starting material, and obviously farlowenthanjhe melting-point of the compound itself.,

These conditions are most clearly expressed in the form shown in Fig. 1,which is a hypothetical melting-point diagram of two starting materials,A- and B, of the type described, and havingmelting-points T1- and-T2,respectively. Inorder to make the illustration wholly generalincharacterJthe basic temperature i's='take'n as T- a As shown, 62% ofstarting materialA reactsfwith 38%of starting material B-to form thecompound AXBy, having a melting-point T3: of approximately T+1400L Thiscompound 'in-turn forms with B a eutectic E1, witha melting-point T4 OfTH-300 and a composition of 25% A and'75 %--B/ With A, AxBy forms aeutectic Eacontaining '70,%A and 30% B} and having a melting-point -TaofT+1300. The-broken line indicates that eutectic formation between AxByand A is not essential;' in case of a compound having an incongruentmelting-point, the temperature of complete fusion ris'es" 'continuouslyfrom T4 to T1, with marked cha'ngein rate at R,- Which is technicallyknown as the reaction point. The above-stated rule nevertheless applies,for AxB -still forms alowmelting product with-B but notlwith-AJ Thisdistinction is fundamentaL Referring again to Fig. 1, and omittingconsideration of the broken line, which applies to only a few cases, itmay be pointed out that'the' curve is the locus of the temperature ofcomplete fusion for everycombination of A and B. Aboveth line, at anycomposition Whatever, the melt is entirely liquid. At the fivecompositions corre spending to A, E2, AxBy} E1" and""B ther-e aredefinite-melting-points, these being T1, T5, T;-,-T4, and T2,respectively, At all other compositions; freezing and melting occur overa range of rem-1 perature. For example, at a composition of 50% each ofA and B, freezing of'jthe wholly molten material begins at about-T-l-1'1'80"; when the com; Pound B n ar te as, a s l d; h s of coursechanges th composition of thereinainf ing liquid, and with a continued'dropj'intemperature more of prey separates until the finalliqurdreaches the composition E1, I at a temperature T4; when itallsolidifies. Similarly, if a melt of: mposition pr ent dbr and, 20%,,Bite; coo1edfifrom'T+2000, for-example, mjss i r rhisl until atemperature of about T+ 1530: is reached, when A begins to separate,again. with a change inliquidcompositiong With furthencooling morle,Afseparates' untillthe liquid. compositionjEzj'is' reached, at a,ternper'ature, T5, when complete, solidification 1 again resu ts;before there Q cariff. 5e.

anyfurth'er' temperaturedrop.

From this discussion it ,will'jbeobyious that. the. hatched; areas inthe, hart represent comfiosi fi tioris which, arecompletelylso'lidatth'e tempe tures shown. simnar1y,"eiear"ar'eas, abdttife curves.- arethose. of complete liquidity,-while stippled areas represent'conditions'of compost tion and temperature inwhich liquid and solid(having different compositions) The actual procedure to be followed incarrying out the principles of this invention may now be explained forthe general case of two starting materials, A and B, again withreference to Fig. 1, Both, it will be observed, are of a refractorycharacter, although it may be assumed that the more refractory materialA is to be the major constituent of the final product. First, one takes25% of A and 75% of B (corresponding to the composition of E1), meltsthe mixture at a temperature T4 (T+300) and allows the product tosolidify. Twenty parts of the crushed product (containing five parts ofA and fifteen of B) are then mixed with eighty parts of A, of any"suitable grain size, and the mixture is formed into the desired shape,rammed into a furnace to form a permanent hearth, or thrown as fettlingmaterial into a hot furnace. When the temperature of the mass is raisedto T+300, thethan that corresponding to AXB no more liquid can formuntil T+l300 (the'melting-point of E2) is reached. Mineralogically, thefinal refractory consists entirely of A and AxBy in equilibrium witheach other; the relative amounts will de-' pend always of course, uponthe proportions of the starting materials used.

In this case, it is evident that a very striking and important resulthas been brought about."

By using two refractory starting materials of the specified type, it hasbeen possible through the application of the present invention to con-"solidate highly refractory particles of A into'a furnace hearth (mass-orshape) at a temperature 1000 degrees below that at which initial liquidformation can subsequently occur, and'in fact 900 degrees below themelting-pointof either starting material.

It is important to observe that the'two start ing materials do not haveto be taken in the exact proportions corresponding to the eutectic E1 inorder to form a low-melting product. -In the case of these two startingmaterials, alarge pro- 7 portion of liquid will be formed at T4 eventhough the composition may be varied, for example, anywhere from 40% Aand 60% B to 12% Aand 88% of liquid E1 at T4 with 52% of solid B,-and-,the

whole mass Will again be molten at T+90Q?, (The proportion of solid andliquid may be determined by measurement from the chart, or may becalculated algebraically; both methods are well known to students ofphase equilibrium 'di'a grams.) j It may also be observed that whentheproportion of starting material Bis greater than 38%;

some liquid will always be formed atTi, the' melting-point of theeutectic E'1,-whereas-'with co-exist in equilibrium. All of this iswellknown to students of phase equilibrium-diagrams, but is mentioned ihere in order to clarify the subsequent discussion.

By the time the reaction is "di B. At the former composition, 59.5% ofliquid E1 will form at T4 with 40.5% of SOHCLAXBL ancl completeliquidity will result at about.T-|-.900?-,=. while at the lattercompositionthere will be 48 %J 38% or less there will be no liquid underthe teiiiperature T5, which is the melting-point of A r/38%: of- B therewill, of course; be none of either eutectic present, and no liquid willbe formed below T3, at which temperature the compound AxBy meltscompletely. The low-melting constituent used in practice must thereforehave a greater proportion of starting material B than is present inAxBy, and the only precaution necessary to eliminate all low-meltingliquid in the ultimate product is to use enough of A in the finalmixture to form the compound AxBy with all of the starting material Bpresent. It may be advantageous to use a much greater proportion of A ifthis particular refractory is superior to AxBy' in the propertiesdesired in the ultimate product.

In all the above discussion consideration has been given to the generalcase. Attention will now be called to combinations of actualstartingmaterials of the same type. These cases are not all equallysimple, but the essential features;-

enumerated above are identical, and such dlfierences as occur will beexplained.

One of the most interesting cases is that of lime and silica (Fig. 2),which have meltingpoints of 2570 and 1728", respectively. They form: ahighly refractory compound, dicalcium silicate (2CaO.SiO2) which has amelting-point of 2130"; The lowest-melting eutectic contains 36% limeand 64% silica, and this melts at 1438, whereas the eutectic betweendicalcium silicate and lime has a, melting-point of 2065, 627 degreeshigher and no liquid can form below this temperature if the proportionof lime to silica is that of di calcium silicate or greater. This casediffers from the one described in Fig. 1 in that there is an in--termediate compound, calcium metasilicate (CaQSiOz) having a,melting-point of 1544 and, strictly speaking, it is this compound whichforms two low-melting eutectics. Both of these eutectics. it may beobserved, have melting-points about 200 degrees below the ordinaryoperatingtem perature of an open hearth or electric steel fur nace,whereas the refractory eutectic between 'dlcalcium silicate and limemelts at a temperature far above any thing used in furnaces of thesetypes.

Of the same type is the melting-point diagram of magnesia and silica, asshown in Fig. 3. The

compound between these two starting materials is the orthosilicate(2MgO.SiO2) forsterlte, which The low-melting, eutectic melts at 154'?and the high-melting" eutectic-between 'forsterite and magnesiawat"1870, 323 degrees higher. The latter temperature has a melting-point of1910".

is at least 200 degrees above ordinary open hearth temperatures, and ifthe magnesia content be high the percentage of liquid formed even atthat temperature is relatively small. Magnesia itself has amelting-point of 2800.

cate has an incongruent melting-point, butthis is of no practicalimportance, and the re'sem-' blance is otherwise quite close. 7

Of some interest (but not illustrated) is the system lime-alumina. Bothof these oxides are highly refractory. In this case there are severalcompounds,- of which the most refractory-is 3CaO.5Al2O3, havingamelting-point of 1735 and forming with'alumina a refractory eutecticmelt- There aretwo low-melting eutectics', that between 3CaO.AlzOa and5CaO.3AlzO3, melt- .ing at 1397, and thatbetween SCaOBAhOaanding at1715".

This case differs" from that of lime and silica in that themetasilisimilar tothat of Fig, 1.

45aand 60 %i alumina,- can, be used satisfactorily:

tttbondv particleslof refractory 1 alumina, and providsidsthattheproportion of alumina in :the mix ture -be atleastthat,in,.3CaO.5A12,Os (75.2%),;n quidcan form below 17 5*.

Qf; substantially different form, but corresp onding somewhat to thatofthe dotted line of Fig, 1,

4Fi ,r4, of alumina and silica. In this case the low mglting eutectic,is exceptional in that. it-

ente s- .a qut 4% f-one a t n m er -.-;thiscase-silica. Itsme1ting-point-is-1550". Then" fractorycompound 3A l2O3 .2Si O2(mullite). has an incongr;uent melting point of I 1830 and olees-loutect cw m n aaw enemeltlng eutectic is eliminated the temperal ilgmipm liquid' -is to increase the; overall 0f ir1itia1 liquid formationisraised by 280 it, Allthat is necessaryto-eliminate the alumina contentto72% or higher, thecomposipgrtedjncomplete detail. The-refractory compgnd ba iumzirconate-lBaQZrOzlhas a-melting:

oint, of at. least-2600,,while the low-melting eutectic containing,about 10% (molecular) of zirconia melts at approximately l300"-.eutectic between ,barium zirconate. and zirconia The has a-,melting;point of approximately 2050, or

n gner 150. degrees.

All-of .theabove :e xamples, both. theoretical. and

raetiqal have dealt with, binary. systems, the twostaigting,materialsbeing in-,;all-. cases. refractory oxides fQExactlythe sameprinciple, however may be applied when there are three startingmaterials, or, to express -theidea differently, when ony.= .,of rthe,starting materials, consists of twooxides whichlmay or, may not,exist-in chemical coin nation With eachother,

,illus tratesfthe general ,case, of three .refractorymxides, A,-B,r-&Ild-, C, having melting-,

points-ofabout, rr+19oo,, T+1600, and ir+2000zv respectively. As before,there is arefractorycompoundAxBy, which-forms a :lowmelting,-.eutecticith-rB orvwith B and ,C, andahigh-melting eutectic with A, orwith A and C. In the presence oi starting material, C themelting-pointsof both binary eutectics .ar e, lowered-somewhat, but it still holdsthatthe lowest-melting eutectic be-, tween- A,,B and c (or, strictly.speaking, between assuming thatsB and -C are taken in constantpropogtions; with-reference to eachotherand tha t lthe two eutectics lieon the same straight llne drawn -through :A to (B+C). This constant;

propgntioneof ,two starting materials, how-ever, is

afrequent commercial condition.

The, pseudobi-nary{melting-point diagram -of A and lliz-i-cnasderivedfrom Fig,;6is shown-in Fig.

7, and it will be observed that it hasa form-very Inthis-casethecompoundAxB (as modified-by the-presence of about 10% of C)melts at about T l-1400, oneeutectic' melts at-T+300 and-the'other-atT+l200-j The principle already explained for -Fig-.;;1 cangbe-ap;

plied in exactly the same way in this caseby.

preforming a low-melting eutectic of A, B -,;and -C.

8:; The; temperatur 10f; tinitial liquid; formation Y therebyraised.909, degrees:

mpassaincfromvthel general o the Specific): One maytalsa S ;ii.-Fig;,8,the two starting ma terialssilica,andscalcined dolomite, andplotthe,

meltin epqint ccurveas a pseudobinary system. It is; seeni,that thecompound dicalcium silicate can, -co,-exist-:with.periclase. Completefusion of a=. low-melting;pro duct, with a silica content of about,,50%lcan ,be made to occur, at 1358,'but. by,--burning;;it.with sufiicientlime to form di-,- calcium;silicate.with all of the silica thus intro-'-dueed;the-temperature-of initial liquid formation,-can;- be raised by622degrees to 1980. This particular, chart does; not show a high-meltingeutectic, since thcwpseudobinary line does notpass -throll l it,-but.such a eutectic neverthe-l, less exists, with; 1980 as its approximatemelting- PQ nt-.,

Anotheri case of a pseudobinary is that of Fig., 9,-whichillustratesrthe sameprinciple when applied-to magnesia, and ahypothetical clay containing silica-and alumina in the proportions .70;to 30., This case is of special interest in that the magnesia-decomposesthe clay to form not one, but; two,-compounds, thesebeing forsterite andspinel (MgOAlzOs), which can co-exist in. equilibrium. Liquid formationcan take place at atemperature as low as 1347, with complete fusion;

at 1362,, yetalllow-rmelting liquids can be eliminated, ;by,.heatingwith suflicientmagnesia, the; temperature ofinitial. liquid formationthen becoming about,\1700, or substantially the melting-point-of, ,puresilica. In products of high; magnesia ,content, -relativelylittle liquidwill be formed, seven at,.this temperature.

It,,is,ob.vio,us-that, if a low-melting rock ormineral-of, suitablecomposition .be available, this may. be, ,used in, place of anartificial, product madebyfusion of the two starting materials. For 1example, both diopside (CaO.MgO.2SiO2) and tremolite ,(CaQBMgOASiOz).melt below 1400, wollastonitew (CaQSiOz) at 1544, cordierite.(ZMgQZAlzOsfiSiOzlat- 1530 and enstatite' (Mgqsiozxat 1547 Theseminerals; are of commOnpccurrencein pyroxenites, amphibolites rand;relatedzrocks,

Now thatl-theuprinciple of the invention has beemfullymxplainedandillustrated, it may beaccurately redefined asa method of consolidat-.incl-refractory; granulan materials, at a relatively low temperature,into masses or shapes of a highly rci factory character, which comprises(a) thesselectionof-two refractory'materials of the type illustrated in;Fig. 1 (or of more than two, as illustratedin Fig. '7), characterized bythe formation :betweemthem-of at least one highly. refractorychemicalcompound, which compound unites pr reacts with, the first but not withthen second-, star ting; material to form anintermediate'pompound,eutectic or other product of rela-' tively lowirefractorinessflb) forming by'any con-- venlentmeans said intermediatecompound, eutec tic; or other product of low refractoriness, orutiliZing-a, natural mineralorrock of similar chemical composition andproperties, (0) using said intermediate product of low refractoriness,while'in amolten condition but at a relatively .low temperature,toconsolidate, particles .cf the second, refractory starting materialinto masses "or; shapes andndl converting. said masses or shapes byvtheapplication of heat intohighly refractory, ceramically, bondedbodiesthrough the substan tlal elimlnation ,of the-said-intermediate prodnotof low refractoriness by means of its reaction with the secondrefractory starting material.

The starting materials must always be of the specific type describedabove, but it is-not essential that, as taken for commercial use, theybe in the particular form mentioned. For example, lime and magnesia havebeen given as starting materials, whereas in practice it may be moreconvenient to use limestone, magnesite, brucite, or "dolomite, all ofwhich on the application of heat are readily converted into thecorresponding oxide or oxides. So also one may use diaspore (A12O3.H2O)as a source of alumina, and barite (BaSOi) of barium oxide, and assources of more than one oxide such minerals as wollastonite, serpentine(3MgO.2ISiO2-2HZO), and kaolinite (AlzO3.2SiO2.2H2O). In every case,however, the combination of oxides chosen must be such that they fallinto the particular type described, There may also be used as a majorstarting. material-a clinker containing magnesia associated with morelimethan that necessary to form dicalciumi silicate with all the silicapresent in it. In such a case, the magnesia is substantially inert andthe excess of lime acts as one starting material, while the other issiliceous, like serpentine, diopside, wollastonite or quartzite.

As already intimated, the initial product of relatively lowrefractoriness need not be a true eutectic between AxBy and the firststarting material. For some applications a low-melting compound such aspseudowollastonite (melting-point 1544) or,5CaO.3AlzOs (melting point1458) may bejsatisfactory. If a considerable proportion of low-meltingproduct is to be used, it is not essen tialrthat it be wholly liquid,but only that the actual quantity of liquid present at the desiredtemperature be sufiicient to consolidate the refractory particles withwhich it is mixed.

Refractoriness is a relative, rather than an absolute, term. Copperrefining furnaces may .be operated at 1100 and copper converters at1250, basic brick may be burned at 1450-1550, open hearth furnaces mayrequire 1650 and electric steel furnaces 1750"; a refractory suitablefor the first two applications might be quite inadequate inrefractoriness for steel production. It is therefore not possible tostate categorically at what temperature low-melting products lyingwithin the scope of this invention should form liquid, but as a generalrule it may be said that the invention relates to low-melting productsforming at least 50% of liquid at 1450, 75% of liquid at 1500, or whollymolten at 1550". It also includes, regardless of the actual temperature,all systems of the type defined when the temperature of consolidation orsetting of the refractory particles by means of a low-melting product isat least 220 degrees centigrade-below the temperature at which liquidformation will occur when equilibrium has been established in theultimate refractory. A large temperature difference of this kind ischaracteristic of the invention, and

thedifierence will usually be substantially greater than 200 degrees.

In discussing systems involving the use of pure starting materials, onecan speak with confidence .as to the temperature of initial liquidformation and the degree of melting. That is not the case, however, whencommercial starting materials are used, for the presence of impuritiesalmost invariably reduces the temperature of liquid formation.Similarly, impurities may make it impossible to eliminate all liquidfrom the final product. It will be evident that some potential sourcesof raw materials, because of theircontent' of im purities, must berejected altogether for application in the practice of this invention.In the practical examples which follow it will be assumed thatimpurities do not occur in the raw materials in sufficient quantity toafiect the re sults to any substantial degree.

The scope of the invention is so broad, and the possible applications ofthe principles involved are so numerous, that the cases mentioned below"are not intended to'do more than provide typical examples. The inventionis by no means limited in scope. by the particulardisclosures madeherein,'but only by thebroad application of the principles involved inthem.

If the low-melting product to be used in the consolidation of refractoryparticles is to-be'preformed, any suitable method of production may beadopted. For example, if dolomite and quartzite areto be used in theproportions'required to produce a material melting below 1400", theoperation can be carried out in an electric'furnac'e,

'or evenin a blast furnace or cupola. The molten product issuing fromthe furnace maybe allowed to solidify and then" be crushed to'thedesired size, or the molten stream may be granulated by breaking it upwith aJ'et of water, steam or air, and allowingthe droplets tofall intoabody of water.

If sin'tering rather than complete fusio'nis desired, a rotary kiln maybe used to'advantage'. Such equipment, with' appropriate temperaturecontrol, can be used for the production of'any low-melting product, andis particularly advantageous when the' product-contains, at thetemvperature of operation, a considerable proportion of solid as well asliquid constituent. Under these conditions the product will usuallyissue from the kiln in the form of clinker, and can be used' with orwithout crushing-according to its particle size.

The use of natural minerals in place of syn- 'thetic low-meltingproducts has'already'bee'n dealt with above.

V v I CaseI There is requireda material for burning in successive layersof .magnesite' tojform the permanent bottom of an open hearth steelfurnace, the object being to replace the magnesite-slag mixture solong-but rather inefiectivelyused for this purpose One may first prepareby the fusion of serpentine, oldfireclay brick and quartzite, alow-melting material containing 20 MgO, 20 A1203 and 60% SiOz. This iscrushed to pass a screen of four-meshes totheinch and is mixed withmagnesiteclinkerof the same grain size-in-proportions of 20 to 80,- andthe mixture is thrown into a hot furnace. As soonas thematerial reachesa temperature of..1350 thelow-melting product fuses! and bonds thehighly refractory particles together.- Subsequent heat treatment of thebot: tom during the, ordinary. burning-in process brings about reactionbetween the constituents and consolidates the mass so that the finalbottom consists of 84 MgC), 4 A1203 and 12% SiOz,

.in the .forni' of periclase, spinel and ,forsterite.

aromas? than burned: dolomite,- be resistant-toslag attack, andibdhardat 1750,".

Two par-tsofraw. dolomite and one'of quartz orsandstone are meltedtoform; a=- slag containing 30 CaO,'21'MgO and 49% SiO2, and-meltingbetween 1350 and 1400. This product is granulated in water, mixed withfour-mesh dolomite (burned without theaddition of iron oxide) in equal:proportion, and the product is used for 'iettiing; Owing to theformation of 50% liquid at1'400 and the immediate-absorptionofthisliquid'by theburn-ed dolomite, setting-is extremely rapid. Theconsolidated product consists exclusively' of periclase anddicalciumsilicata'and forms no liquid below 19.80% Since the slagconsists=:-almost exclusively of dicalcium and tricalciumvsilicate,with-a little calcium carbide, caleium fiuoride, magnesia, and otherminor constituents,- it" has no actiononthe'banks. (If desired,thedolomitecould be used raw, but it- IS usually more economicaltopreburn'it. If desired;- one'could alsoadd 'tothe final mixture asmall proportion of calcium phosphate orother suitable stabilizing agentto prevent the subsequent dusting of the dicalcium silicate on cooling,but this is a refinement which does notappreciably affect'the procedureor productgand does notconstituteia part of the present invention.)

As to the behaviour of such a fettling material under the action ofheat, it'may be said that until initial: fusion takes place the.granular masson the-banks is soft and friable, as when originally mixed;The appearance of liquid produces in the mass'a mushy condition; likethat of wet snow. 'As-the form'ationofrefractory compounds proceeds, themass becomes progressively'harder -'anddrier-,and when the reaction; iscomplete the consolidated material is usually 'very hard, with no =si'gn'ofliquid. With-differentstarting materials-,- -the change in characterof the material used "for fettling varies somewhat, owing todifferehces: in the amount: and viscosity-of the; liq;- uid present, therate at which theyflnal reactions proceed, and other factors.Frequently, however, materials of the type described will pass through"all, "of, these. stages befor O n ry fettling fractories show an'y'signoffsetting whatever.

Case-3 Difiiculty is encountered in burning 'zir'conia brick, owing tothe high temperature required for the development of a bond'to providethe necessary. strength in; the final product. Some means are requiredof'producin'g a bond at a lower "temperature, and at the same timeofdeveloping a stronger b'rick,fo'f adequate refractoriness.

"Oneilrst, prepares a eutectic containing 90 BaO "and 10% ZrO2, andthe'n introduces 10% 'of this, "a'sja fine constituent, into granularzirconia to be used in making brick. The molded; brick are burned at1400, a temperature easily attainable in any refractory brick'kiln. At1350 the eutectic melts, and when reaction with the 'zirconia andconsolidation are complete a strong ceramic bond is'efie'cted, and noliquid can, form below 2030, a refractoriness which is. more thanadequate. In, a. similar way, forsterite, mullite, and other types ofbrick of excellentstrength and high refractoriness can, be made atrelatively low tend,- neretures.

Case 4 -.practice, the furnace is-heated to... working temperature andthen cooled before putting; in the first charge. Cracks form, owingtothermal con traction, and steel would subsequently penetrate these,weakening the bottom and increasing its thermal conductivity. There isrequired a refractory material with which the cracks canb'e filled toprevent the penetration of steel.

Instead of preparing a highly refractory material and attempting to fillthe cracks with it (which would be practically impossible) one picparesa low-melting product by .sintering ina rotarykiln at a temperature of1400 a mixture of serpentine, clay, and kyanite to make a productcontaining 17 MgO, 36 A1203, and 47% S102. At this temperature there isgood clinkering action without complete fusion. The furnace is heated to1500 and sufiicient ofthe crushed sinter is then thrown into it,especially along the cracks, to fill them. adequately, with some excess.The material immediately melts and runs into; the cracks, where itslowly reacts with the magnesia walls to-form forsterite and spinel,havingmelt ingpointsof 1910 and 2135, respectively. These refractorycompounds will remain solid atfthe highest; temperature of the furnace,and by con.- solidating the whole bottom, effectively prevent thepenetration of steel or slag.

Case 5 It is desired to lower the setting temperature of one of thecommon thermoplastic fettlingrefractories which, in spite of itscontent. of calcium ferriteand aluminata inthe absence or slag re;-mains in a loose condition on the furnace banks until the temperaturerises above 1600. It is also an objective to increase the ultimatemartian;- ness of this material, which. is definitely plastic @1650 a VI The thermoplastic refractory contains (exclue sive of its dead-burningagents, which may for the moment be regarded as impurities)approxima'tely 12 MgO, 21 CaO and 7%. S102. Sincetlie lime contentis,approximately 60% -greater than that required to form the refractorycompound dicalciurnfsilicate, the magnesia may be takenas periclase andneglected in the calculation of siliceous flux'to be added; hence thesystem is essentially binary. There is-available as a low;- meltingmaterial a quantity of the mineral diopside (CaO.MgO.2SiOz). Enough ofthis will. be added to form in the final product only dicalcium silicatefrom all lime and silica present. Calculation shows that the quantityrequired is 8.5 parts, which will be used with 91.5 parts of thethermoplasticrefractory. The diopside is crushed to 20 mesh, mixed withthe thermoplastic refractory, and thrown. onto the banks of an openhearth furnace. as a fettling material. The diop side melts at 1395,thereby lowering the setting temperature by more than 200. degrees, andsubsequently reacts. with and consolidates thethermoplastic refractoryto bring about a substantial increase in its refractoriness. Both ofthese results are, important advantages. (Actually, the addition of thesiliceous low-melting diopside breaks up the calcium ferrite andaluminateQa nd replaces them with more refractory dicaljci um silicate,magnesium ferrite and magnesium amminate (spinel), but the eliminationof these fluxes is not a part of the invention.)

This procedure i in striking contrast with the practice, disclosed inthe prior art, of adding, a

material high in lime to refractories which are, to

some degree thermoplastic due to-the presence in, them of orthosilicatesof-low refractoriness (monticellite and merwinite). The new methodgreatly lowers the setting temperatures of the major refractory byproviding a siliceous, lowmelting material between the grains to bebonded, instead of actually raising the setting temperature byintroducing between the plastic grains a calcareous material of highrefractoriness. The consolidating reaction between the liquid lowmelting constituent and the highly refractory particles readily takesplace under normal burning conditions.

I claim:

1. A method of consolidating refractory materials, which comprisesmixing discrete particles comprising essentially refractory oxidematerial from a group consisting of lime, magnesia, alumina and zirconiawith non-refractory material comprising essentially a low-meltingcompound of said oxide and being one of a group consisting oi calciumsilicate and calcium magnesium silicate when said oxide is lime and limewith magnesi-a present, magnesium silicate and magnesium aluminumsilicate when said oxide is magnesia, barium zircon-ate when said oxideis zirconia, and aluminum silicate when said oxide is alumina, saidnon-refractory material becoming liquid at a temperature between 1321and 1550 C., the mixture containing not less than 50% by weight of saiddiscrete particles, and heating the mixture to not less than 1321 C. tomelt said nonrefractory material, and thus consolidate said particlesinto a highly refractory mass.

2. A method of consolidating refractory materials which comprisesforming an intimate mixture of two types of materials, the first typebeing granular particles consisting essentially of refractory oxidematerial from a group consisting of lime, magnesia, alumina andzirconia, and the second type comprising essentially a low-meltingcompound of the oxide material and being one 01' a group consisting ofcalcium silicate and calcium magnesium silicate when the oxide materialis lime and lime with magnesia present with the molecular ratio of limeto silica in the mixture not less than 2.0, magnesium silicate when theoxide material is magnesia with the molecular ratio of magnesia tosilica in the mixture not less than 2.0, magnesium aluminum silicatewhen the oxide material is magnesia with a molecular ratio of magnesiato silica in the mixture not less than 2.0 and additional magnesia toalumina not less than 1.0, aluminum silicate when the oxide material isalumina with the molecular ratio of alumina to silica in the mixture notless than 1.5, and barium ziroonate when the oxide material is zlrconiawith the molecular ratio of zirconia to baryta in the mixture not lessthan 1.0, and heating the mixture to not less than 1321 C. to melt saidnon-refractory compound and thus consolidate said particles into ahighly refractory mass,

3. A method as defined in claim 1 wherein the non-refractory compound isa preformed material.

4. a method as defined in claim 1 wherein the 65 method is carried outin a furnace lining.

5. A batch material for refractory masses and shapes, which comprises anintimate mixture of discrete particles comprising essentially refractoryoxide material from a group consisting of 14 lime, magnesia, alumina andzirconia, and nonrefractory material comprising essentially a lowmeltingcompound of said oxide material and being one of a group consisting of(a) calcium silicate and calcium magnesium silicate when the oxidematerial is lime and lime with magnesia, (1)) magnesium silicate andmagnesium aluminum silicate when the oxide material is magnesia, (0)aluminum silicate when the oxide material is alumina, (d) bariumzirconate when the oxide material is zirconia, and said mixturecontaining not less than 50% by weight of said discrete particles,whereby when the mixture is heated to liquefy said non-refractorymaterial the whole 0 mass consolidates into a product which does notmelt below 1800 C.

6. A batch material for refractory masses and shapes, which comprises anintimate mixture of two types of materials, the first type beinggranular particles consisting essentially of refractory oxide materialfrom a group consisting of lime, magnesia, alumina, and zirconia, andthe second type consisting essentially of a low-melting compound of therefractory oxide and being one of a group consisting of (a) calciumsilicate and calcium magnesium silicate when the oxide is lime and limewith magnesia present with the molecular ratio of lime to silica in themixture not less than 2.0, (1)) magnesium silicate when the oxide ismagnesia with the molecular ratio in the mixture not less than 2.0, (0)magnesium aluminum silicate when the oxide is magnesia with a molecularratio of magnesia to silica in the mixture not less than 2.0 andadditional magnesia to alumina not less than 1.0, ((1) aluminum silicatewhen the oxide is alumina with the molecular ratio of alumina to silicain the mixture not less than 1.5 and (e) barium zirconate when the oxideis zirconia and the molecular ratio of zirconia, to baryta in themixture not less than 1.0, whereby when the mixture is heated to liquefysaid non-refractory material the whole mass consolidates into a productwhich does not melt below 1800 C.

7. A method as defined in claim 2 wherein the mixture is heated to atemperature of not less than 1550 C. to melt the non-refractory materialand thus consolidate the particles into a highly refractory mass.

FRANK EUGENE LATHE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,300,631 Meyer Apr. 15, 19192,015,446 Cape et al Sept. 24, 1935 so 2,089,970 Lee Aug. 17, 19372,207,557 Sell July 9, 1940 2,238,428 Seaton et a1 Apr. 15, 1941 FOREIGNPATENTS Number Country Date 396,532 Great Britain 1933 OTHER REFERENCESMay 11, 1943.

1. A METHOD OF CONSOLIDATING REFRACTORY MATERIALS, WHICH COMPRISESMIXING DISCRETE PARTICLES COMPRISING ESSENTIALLY REFRACTORY OXIDEMATERIAL FROM A GROUP CONSISTING OF LIME, MAGNESIA, ALUMINA AND ZIRCONIAWITH NON-REFRACTORY MATERIAL COMPRISING ESSENTIALLY A LOW-MELTINGCOMPOUND OF SAID OXIDE AND BEING ONE OF A GROUP CONSISTING OF CALCIUMSILICATE AND CALCIUM MAGNESIUM SILICATE WHEN SAID OXIDE IS LIME AND LIMEWITH MAGNESIA PRESENT, MAGNESIUM SILICATE AND MAGNESIUM ALUMINUMSILICATE WHEN SAID OXIDE IS MAGNESIA, BARIUM ZIRCONATE WHEN SAID OXIDEIS ZIRCONIA, AND